pushkin-compiler 0.1.0

//! Parsing + constrained-subset validation of the canonical JSON Schema.
//! The subset is deliberately small in Phase 1: strict objects with string
//! properties (length/format/enum constraints). Everything else is rejected
//! by name with alternatives.

use crate::CompileError;

/// Constructs the Phase 1 subset does not carry, with the alternative named
/// in the rejection (spec §5.1 — never silently dropped).
const UNREPRESENTABLE: &[(&str, &str)] = &[
    ("patternProperties", "declare explicit 'properties' instead"),
    (
        "prefixItems",
        "declare a named object; tuples do not round-trip to SQL",
    ),
    (
        "$ref",
        "inline the definition; cross-schema refs land in a later phase",
    ),
    ("allOf", "flatten the composition into one object"),
    ("anyOf", "split into separate contracts"),
    ("oneOf", "split into separate contracts"),
    ("not", "express the constraint positively"),
];

const SUPPORTED_FORMATS: &[&str] = &["email"];

/// Keywords the parser consumes at the top level. The gate is BIJECTIVE
/// (F26): a keyword outside this set is rejected by name, never
/// tolerated-and-ignored. Tolerating an unconsumed keyword was a silent
/// DROP before the typify swap and, after it, silent cross-target DRIFT
/// — `targets/rust.rs` feeds typify the RAW schema JSON, so a keyword
/// the parser ignores still shapes the Rust binding alone.
const TOP_LEVEL_KEYWORDS: &[&str] = &[
    "$schema",
    "$comment",
    "type",
    "properties",
    "required",
    "additionalProperties",
];

/// Keywords the parser consumes on a property subschema (F26).
const PROPERTY_KEYWORDS: &[&str] = &[
    "type",
    "minLength",
    "maxLength",
    "format",
    "enum",
    "default",
    "pattern",
];

/// The email regex the authoring pipeline (Zod v4 `z.email()`) emits
/// alongside `format: "email"`. `pattern` is admitted ONLY as this
/// format's companion and ONLY byte-equal to this constant (human
/// decision, recorded §7).
///
/// A future authoring-library bump that changes the emitted regex will
/// fail compile loudly here. That is the DESIGNED behavior, not a bug:
/// the alternative is the silent cross-target drift this gate closes.
/// Remediation is a deliberate constant update in the same PR as the bump.
const AUTHORING_EMAIL_PATTERN: &str = r"^(?!\.)(?!.*\.\.)([A-Za-z0-9_'+\-\.]*)[A-Za-z0-9_+-]@([A-Za-z0-9][A-Za-z0-9\-]*\.)+[A-Za-z]{2,}$";

#[derive(Debug, Clone, PartialEq)]
pub enum PropertyKind {
    String {
        min_length: Option<u64>,
        max_length: Option<u64>,
        format: Option<String>,
        enum_values: Option<Vec<String>>,
        default: Option<String>,
    },
}

#[derive(Debug, Clone, PartialEq)]
pub struct Property {
    pub name: String,
    pub kind: PropertyKind,
    pub required: bool,
}

#[derive(Debug, Clone)]
pub struct ContractSchema {
    pub contract_name: String,
    pub properties: Vec<Property>,
}

pub fn parse(contract_name: &str, schema_json: &str) -> Result<ContractSchema, CompileError> {
    let value: serde_json::Value =
        serde_json::from_str(schema_json).map_err(|error| CompileError::InvalidSchema {
            message: error.to_string(),
        })?;

    require_identifier("contract name", contract_name)?;
    reject_unrepresentable(&value)?;
    reject_unknown_top_level_keywords(&value)?;
    require_strict_object(&value)?;

    let required = required_names(&value)?;
    let properties = parse_properties(&value, &required)?;

    Ok(ContractSchema {
        contract_name: contract_name.to_owned(),
        properties,
    })
}

/// Walks the schema keyword-aware: keys of a schema object are keywords and
/// are matched against the unrepresentable list, but the keys of a
/// `properties` map are user-defined property NAMES — data, not structure —
/// so only their values (subschemas) are walked (S1).
fn reject_unrepresentable(value: &serde_json::Value) -> Result<(), CompileError> {
    match value {
        serde_json::Value::Object(map) => {
            for (key, child) in map {
                if let Some((construct, alternative)) = UNREPRESENTABLE
                    .iter()
                    .find(|(construct, _)| *construct == key)
                {
                    return Err(CompileError::Unrepresentable {
                        construct: (*construct).to_owned(),
                        alternatives: (*alternative).to_owned(),
                    });
                }
                if key == "properties" {
                    if let Some(properties) = child.as_object() {
                        for subschema in properties.values() {
                            reject_unrepresentable(subschema)?;
                        }
                        continue;
                    }
                }
                reject_unrepresentable(child)?;
            }
        }
        serde_json::Value::Array(entries) => {
            for entry in entries {
                reject_unrepresentable(entry)?;
            }
        }
        _ => {}
    }
    Ok(())
}

/// F26: the top-level counterpart to the property allowlist. Runs AFTER
/// `reject_unrepresentable` so the named constructs keep their
/// `Unrepresentable` variant and their specific alternatives.
///
/// `parse` has already parsed the document, and a non-object top level is
/// rejected by `require_strict_object`; the empty-map case simply finds
/// no unknown key.
fn reject_unknown_top_level_keywords(value: &serde_json::Value) -> Result<(), CompileError> {
    for key in value.as_object().into_iter().flatten().map(|(key, _)| key) {
        if !TOP_LEVEL_KEYWORDS.contains(&key.as_str()) {
            return Err(CompileError::Unrepresentable {
                construct: format!("top-level keyword '{key}'"),
                alternatives: format!(
                    "the subset carries {}; annotation keywords are not \
                     emitted to any target, so carrying them would drift \
                     the bindings — remove it, or propose it as a \
                     widening step",
                    TOP_LEVEL_KEYWORDS.join(", ")
                ),
            });
        }
    }
    Ok(())
}

/// F26: a property keyword the parser does not consume would reach
/// typify through the raw-JSON feed and shape the Rust binding ONLY.
///
/// Called from `parse_string_property` after its `type` check, so `spec`
/// is always an object here.
fn reject_unknown_property_keywords(
    name: &str,
    spec: &serde_json::Value,
) -> Result<(), CompileError> {
    for key in spec.as_object().into_iter().flatten().map(|(key, _)| key) {
        if !PROPERTY_KEYWORDS.contains(&key.as_str()) {
            return Err(CompileError::Unrepresentable {
                construct: format!("keyword '{key}' on property '{name}'"),
                alternatives: format!(
                    "the subset carries {}; remove it, or propose it as a \
                     widening step",
                    PROPERTY_KEYWORDS.join(", ")
                ),
            });
        }
    }
    Ok(())
}

/// F26(b), human decision: `pattern` is admitted ONLY as the email
/// format's companion, byte-equal to what the authoring pipeline emits.
/// Zod/Pydantic/SQL carry no pattern handling, so any other pattern
/// would be enforced in Rust alone — the exact drift this closes.
fn validate_pattern(
    name: &str,
    spec: &serde_json::Value,
    format: Option<&str>,
) -> Result<(), CompileError> {
    let Some(value) = spec.get("pattern") else {
        return Ok(());
    };
    let Some(pattern) = value.as_str() else {
        return Err(invalid_property_keyword(name, "'pattern' must be a string"));
    };
    if format == Some("email") && pattern == AUTHORING_EMAIL_PATTERN {
        return Ok(());
    }
    Err(CompileError::Unrepresentable {
        construct: format!("'pattern' on property '{name}'"),
        alternatives: "format 'email', or propose pattern support as a widening step".to_owned(),
    })
}

fn require_strict_object(value: &serde_json::Value) -> Result<(), CompileError> {
    if value.get("type").and_then(serde_json::Value::as_str) != Some("object") {
        return Err(CompileError::InvalidSchema {
            message: "top-level schema must be an object type".to_owned(),
        });
    }
    if value.get("additionalProperties") != Some(&serde_json::Value::Bool(false)) {
        return Err(CompileError::InvalidSchema {
            message: "additionalProperties must be false (strictness is mandatory, charter N2)"
                .to_owned(),
        });
    }
    Ok(())
}

fn required_names(value: &serde_json::Value) -> Result<Vec<String>, CompileError> {
    let Some(required) = value.get("required") else {
        return Ok(Vec::new());
    };
    let Some(entries) = required.as_array() else {
        return Err(invalid_keyword("required", "must be an array of strings"));
    };
    entries
        .iter()
        .map(|entry| {
            entry
                .as_str()
                .map(str::to_owned)
                .ok_or_else(|| invalid_keyword("required", "entries must all be strings"))
        })
        .collect()
}

fn parse_properties(
    value: &serde_json::Value,
    required: &[String],
) -> Result<Vec<Property>, CompileError> {
    let Some(map) = value
        .get("properties")
        .and_then(serde_json::Value::as_object)
    else {
        return Err(CompileError::InvalidSchema {
            message: "schema declares no properties".to_owned(),
        });
    };
    let mut properties = Vec::new();
    for (name, spec) in map {
        require_identifier("property name", name)?;
        let kind = parse_string_property(name, spec)?;
        let required = required.contains(name);
        reject_required_with_default(name, &kind, required)?;
        properties.push(Property {
            name: name.clone(),
            kind,
            required,
        });
    }
    Ok(properties)
}

/// `required` means the caller MUST send the key; `default` means fill it
/// when omitted — emitted together every target silently demotes the field
/// to optional (S5 human decision, option a: loud rejection, never a quiet
/// winner).
fn reject_required_with_default(
    name: &str,
    kind: &PropertyKind,
    required: bool,
) -> Result<(), CompileError> {
    let PropertyKind::String { default, .. } = kind;
    if required && default.is_some() {
        return Err(CompileError::InvalidSchema {
            message: format!(
                "property '{name}' is both required and has a default; \
                 choose one: required (caller must send it) or \
                 default (caller may omit it)"
            ),
        });
    }
    Ok(())
}

/// Names are emitted verbatim into TS, Python, Rust, and SQL identifiers
/// (S2): only `^[A-Za-z_][A-Za-z0-9_]*$` is portable across all four
/// without renaming machinery, which is out of scope by decision.
fn require_identifier(role: &str, name: &str) -> Result<(), CompileError> {
    let mut chars = name.chars();
    let valid = chars
        .next()
        .is_some_and(|first| first.is_ascii_alphabetic() || first == '_')
        && chars.all(|rest| rest.is_ascii_alphanumeric() || rest == '_');
    if valid {
        return Ok(());
    }
    Err(CompileError::InvalidSchema {
        message: format!(
            "{role} '{name}' is not a portable identifier; \
             names must match [A-Za-z_][A-Za-z0-9_]* to emit into all targets"
        ),
    })
}

fn parse_string_property(
    name: &str,
    spec: &serde_json::Value,
) -> Result<PropertyKind, CompileError> {
    let type_name = spec.get("type").and_then(serde_json::Value::as_str);
    if type_name != Some("string") {
        return Err(CompileError::Unrepresentable {
            construct: format!("property '{name}' of type {type_name:?}"),
            alternatives: "Phase 1 subset carries string properties; widen in a later phase"
                .to_owned(),
        });
    }
    reject_unknown_property_keywords(name, spec)?;
    let format = parse_format(name, spec)?;
    validate_pattern(name, spec, format.as_deref())?;
    let enum_values = parse_enum(name, spec)?;
    let default = parse_default(name, spec)?;
    if let (Some(values), Some(value)) = (&enum_values, &default) {
        if !values.contains(value) {
            return Err(invalid_property_keyword(
                name,
                "'default' must be one of the declared 'enum' values",
            ));
        }
    }
    Ok(PropertyKind::String {
        min_length: spec.get("minLength").and_then(serde_json::Value::as_u64),
        max_length: spec.get("maxLength").and_then(serde_json::Value::as_u64),
        format,
        enum_values,
        default,
    })
}

fn parse_format(name: &str, spec: &serde_json::Value) -> Result<Option<String>, CompileError> {
    let Some(value) = spec.get("format") else {
        return Ok(None);
    };
    let Some(format) = value.as_str() else {
        return Err(invalid_keyword("format", "must be a string"));
    };
    if !SUPPORTED_FORMATS.contains(&format) {
        return Err(CompileError::Unrepresentable {
            construct: format!("format '{format}' on property '{name}'"),
            alternatives: "format 'email', or omit 'format'".to_owned(),
        });
    }
    Ok(Some(format.to_owned()))
}

fn parse_enum(name: &str, spec: &serde_json::Value) -> Result<Option<Vec<String>>, CompileError> {
    let Some(value) = spec.get("enum") else {
        return Ok(None);
    };
    let Some(entries) = value.as_array() else {
        return Err(invalid_property_keyword(name, "'enum' must be an array"));
    };
    entries
        .iter()
        .map(|entry| {
            entry
                .as_str()
                .map(str::to_owned)
                .ok_or_else(|| invalid_property_keyword(name, "'enum' entries must all be strings"))
        })
        .collect::<Result<Vec<_>, _>>()
        .map(Some)
}

fn parse_default(name: &str, spec: &serde_json::Value) -> Result<Option<String>, CompileError> {
    let Some(value) = spec.get("default") else {
        return Ok(None);
    };
    value.as_str().map(str::to_owned).map(Some).ok_or_else(|| {
        invalid_property_keyword(name, "'default' must be a string for a string property")
    })
}

fn invalid_keyword(keyword: &str, detail: &str) -> CompileError {
    CompileError::InvalidSchema {
        message: format!("'{keyword}' {detail}"),
    }
}

fn invalid_property_keyword(name: &str, detail: &str) -> CompileError {
    CompileError::InvalidSchema {
        message: format!("property '{name}' keyword {detail}"),
    }
}